Intraocular pressure and tonometry Flashcards
(15 cards)
what is intraocular pressure?
the pressure with the eyeball occurring as a result of the constant formation and drainage of aqueous humour
iop and ah
produced by cillary epithelium
drains via two routes
trabecular mesh work
uveoscleral route
too high iop
ocular hypertension
leads to glaucoma
too low iop
ocular hypotension
inflammation, retinal choroidal detachment, after surgery
- reduced VA
normal range of iop
10 - 21 mmHg
treating glaucoma
lower iop
eye drops
surgery
how to measure iop?
measure how much pressure is needed to flatten cornea
contact tonometry
- probe makes contact with cornea directly
- requires anaesthetic drops
- optometrists, ophthalmologists and ophthalmic nurses do it
- the known area of probe applies pressure to cornea to work out intraocular pressure
goldmann tonometer- gold standard as most accurate needs a slit lamp
perkins- handheld tonometer
non-contact tonometry
- does not contact with eye
- no anaesthetic required
- operated by wider range of staff
- you sit at machine and look at light
- machine releases quick puff of air onto cornea
- measures how the cornea flattens in response and then calculates iop
- requires careful alignment
Why isn’t NCT the gold standard?
- less reliable
- often over-read at higher range
- NICE requires referral for glaucoma based in iop alone ti be based on goldmann tonometry
Cant we just measure iop to detect glaucoma?
not everyone with glaucoma has a high iop
short term variability
changes in iop short term instantly
breathing
eye movement
medium term variability
days to weeks
posture
medication
lying down
iop naturally higher in morning
long term variability
months or years
age
smoking
diabetes
inaccurate measurements
corneal thickness
corneal curvature
